1. Technical Field
The present disclosure relates to a balancing technology of a battery cell module, and more particularly, a battery cell balancing method which is capable of balancing a plurality of battery cells of which the stored charges are not equal, in a battery cell balancing circuit using LC series resonance circuit.
2. Related Art
In general, when a voltage across a battery cell exceeds a predetermined value, the battery cell is likely to explode, and when the voltage falls below a predetermined value, the battery cell is likely to receive permanent damage. Since a hybrid electric vehicle or notebook computer requires a power supply with a relatively large capacity, a battery cell module (battery pack) including a plurality of battery cells connected in series is used to supply power. However, when such a battery cell module is used, a voltage imbalance may occur due to a difference in performance among the battery cells.
When one battery cell within the battery cell module reaches the upper limit voltage before the other battery cells while the battery cell module is charged, the battery cell module cannot be charged any more. Thus, the charging operation must be ended in a state where the other battery cells are not sufficiently charged. In this case, the charge capacity of the battery cell module may not reach the rated charge capacity.
Furthermore, when one battery cell within the battery cell module reaches the lower limit voltage before the other battery cells while the battery cell module is discharged, the battery cell module cannot be used any more. Thus, the use time of the battery cell module is reduced as much.
Therefore, when the battery cell module is charged or discharged, the electrical energy of a battery cell having relatively high electrical energy may be supplied to another battery having relatively low electrical energy, in order to improve the use time of the battery cell module. Such an operation is referred to as battery cell balancing.
FIG. 1 is a circuit diagram of a conventional battery cell balancing circuit using parallel resistors. As illustrated in FIG. 1, the conventional battery cell balancing circuit includes a battery module 11 including battery cells CELL1 to CELL4 connected in series, resistors R11 to R14 connected in series, and switches SW11 to SW15 configured to selectively connect the battery cells CELL to CELL4 of the battery module 11 to the resistors R11 to R14.
Referring to FIG. 1, when the charge voltage of an arbitrary battery cell among the battery cells CELL1 to CELL4 within the battery module 11 reaches the upper limit voltage before the charge voltages of the other battery cells while the battery module 11 is charged, the corresponding switch among the switches SW11 to SW15 is turned on to discharge the battery cell through the corresponding resistor among the resistors R11 to R14.
FIG. 2 is a circuit diagram of a conventional battery cell balancing circuit using capacitors. As illustrated in FIG. 2, the conventional battery cell balancing circuit includes a battery module 21 including battery cells CELL1 to CELL4 connected in series, capacitors C21 to C23 connected in series, and switches SW11 to SW15 configured to selectively connect the capacitors C21 to C23 to the battery cells CELL to CELL4.
Referring to FIG. 2, the battery cell balancing circuit using the capacitors has two kinds of connection states. In a first connection state, one terminal of the capacitor C21, a connection terminal between the capacitors C21 and C22, a connection terminal between the capacitors C22 and C23, and the other terminal of the capacitor C23 are connected to one terminals (anode terminals) of the battery cells CELL1 to CELL4, respectively, as illustrated in FIG. 2. In a second connection state, the one terminal of the capacitor C21, the connection terminal between the capacitors C21 and C22, the connection terminal between the capacitors C22 and C23, and the other terminal of the capacitor C23 are connected to the other terminals (cathode terminals) of the battery cells CELL1 to CELL4, respectively.
FIG. 3 is a circuit diagram of a conventional battery cell balancing circuit using a flyback structure. As illustrated in FIG. 3, the conventional battery cell balancing circuit includes a battery module 31 including battery cells CELL1 to CELL4 connected in series, a flyback converter 32, and switches SW31 to SW35 configured to selectively connect a plurality of secondary coils of the flyback converter 32 to the battery cells CELL to CELL4, respectively.
The battery cell balancing circuit of FIG. 3 is a battery cell balancing circuit using a flyback structure which is one of switch mode power supplies (SMPS). The battery cell balancing circuit can transfer electrical energy to the battery cells CELL1 to CELL4 connected in series within the battery module 31 using the switches SW31 to SW34, and transfer electrical energy between both terminals of the battery module 31.
However, the conventional battery cell balancing circuit is configured to repeat an operation of recovering charge from the battery cell storing the highest charge and supplying the recovered charge to the battery cell storing the lowest charge.
Thus, when there exist a plurality of battery cells of which the stored charges are not equal, the conventional battery cell balancing circuit has difficulties in completing balancing all of the battery cells, and requires a large amount of balancing time, which makes it possible to degrade the efficiency of the balancing operation.